Thread Bar Project, nothing is going right and I need help

Sorry I am late to the party. It has been a week of hospital visits and doctor appointments. When I was in school we had to complete a 4 step threading exercise twice each grade period, so 8 a year for 4 years. The threads changed from 4 basic sizes to left hand, acme and finally dual lead. Here is what I learned;

1) Work carefully and think things through
2) Face your stock and drill you center holes in one lathe. (see #1)
3) Before you turn between centers make sure you align the tailstock with a dial indicator and test bar. (see #1)
4) Rough your thread sizes but do not turn to final diameter until you are on the lathe you will thread that section on. (see #1)
5) Do not start to cut a thread unless you can finish during that class. (see #1)
6) Make sure you have your threading tool sharp and square to the work. (see #1)

As far as center drills use what you have, its not a problem unless you don't drill deep enough to get a taper or you go too deep and get a counterbore, (see #1). With the size of the threads/stock your using it would be very difficult to put on too much pressure with the center, (see #1). Standard 60* threads can be cut advancing with the cross slide or using the compound at 29.5*; I like the compound because it cuts with only one edge of the tool and I seem to get a better finish. When I am close I usually take very small clean up passes with the cross slide, (see #1)

I am a semi retired teacher, not in machine shop but in a technical college; part of what needs to be taught/learned/evaluated is how to sort out problems. Ask anyone here how often critical thinking and problem solving is used in the shop; (this is #1 !)

You will get this, perhaps not this time, but please see #1.
 
It might be worth noting that if you are getting substandard threads using the cross slide, either the tool is not on center or it is improperly ground. One of my first real-life lessons in machining came about 50 years ago from a 90-some year old machinist, when he asked why I was using the compound slide to thread a cast iron part. At that time, I had never seen it done any other way. His lesson was that feeding using the compound was a workaround for threading stringy materials like hot rolled steel. Years later, I was able to use this lesson to revise NC tapes (yeah, really.... tapes!) to thread hard materials using a 90° feed. The particular hardened part was knocking the tip off of carbide inserts at an alarming rate. Feeding straight in fixed the issue.

[opinion]
Personally, I'm a bit concerned that the instructor is letting you teach yourself. He should be an active part of your instruction: observing, offering advice, and explaining the process and the physics involved..... I'll be the first person to note that learning is not a spectator sport, but you are paying his salary. He needs to earn it.
[/opinion]
 
Thanks for the long comment. I appreciate it. I made one more mistake with this bar and have to start over yet again. I finally set my tool height and everything was right, but completely ignored the 29.5 degree on the compound, something I did every time, just not this time. Anyways, I center drilled a new piece. While I was center drilling, the chuck in the tailstock moved to the right. It didn't move per say, but like twisted very slightly while I was cutting. It wasn't the drill chuck that was loosen, it was the head. Do you think this is a scrap piece now since it twisted to the right as I was cutting or should I be OK with it? If I can turn it down and it holds concentricity I am probably fine correct? Thanks guys.!
 
Chuck in tail stock moved/rotated. Not good, could gall the Morse taper in the tail stock, causing non concentric with spindle condition.
Remove chuck, check for metal attached to taper. If it's galled, well. it should be fixed. If it's not, forget about it. Go ahead and work on your part.
 
chips&more said:
Turn your compound so its travel is the same as the work direction. Turn the lathe on engage the half nuts have the tool bit over the work. Turn off the lathe. Dial the compound and cross until the tool bit aligns perfectly with the thread you are trying to catch. Now retract the tool bit with the cross slide. Do not touch/turn the compound anymore. Just feed the cross until the job is done…Good Luck, Dave.
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Picking up an existing thread with a CNC lathe is a different kettle of dead stinking fish.

An encoder tells the control how to move the tool in relation to the spindle orientation, there is no gear train, you can not stop the feed once started so even if you E-stop it the spindle and tool go out of sync. The only way that I have done it is to jog the tool into the thread and note the Z Axis dimension, adjust the start Z Axis input in the correct direction and run it with the tool slightly inside the thread and run as slow as possible and eyeball it. Repeat again and again until you have it, this is very very time consuming. The few circumstances where this may be required are in the event of a power failure/control lockup or error such as a low lube oil shut down, assuming that the part wasn't ruined when the tool stopped moving but the spindle carried on rotating, this will also break the insert. If the shut down occurs when the tool is in a rapid move on the way back for the next pass then you are fortunate indeed.

I have found picking up an existing thread far faster on a manual lathe.
 
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I will check with a test bar to make sure it runs concentric but I should be OK right? Thank you.
 
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Wreck™Wreck said:
Picking up an existing thread with a CNC lathe is a different kettle of dead stinking fish.

An encoder tells the control how to move the tool in relation to the spindle orientation, there is no gear train, you can not stop the feed once started so even if you E-stop it the spindle and tool go out of sync. The only way that I have done it is to jog the tool into the thread and note the Z Axis dimension, adjust the start Z Axis input in the correct direction and run it with the tool slightly inside the thread and run as slow as possible and eyeball it. Repeat again and again until you have it, this is very very time consuming. The few circumstances where this may be required are in the event of a power failure/control lockup or error such as a low lube oil shut down, assuming that the part wasn't ruined when the tool stopped moving but the spindle carried on rotating, this will also break the insert. If the shut down occurs when the tool is in a rapid move on the way back for the next pass then you are fortunate indeed.

I have found picking up an existing thread far faster on a manual lathe.
Click to expand...
OK, thanks for that insite. Don’t have CNC, only a manual lathe and probably will never own a CNC lathe any time soon. Maybe a CNC mill one of these days:grin:. But thanks again, I’ll try and remember not to go chasing a thread on a CNC lathe…Dave
 
Was not directed toward you, merely an addition to the "picking up an existing thread" discussion above. unrelated to the original post yet is about threading with a lathe, relax.
 
the first link didn't work and the second link doesn't really help me. we are doing 60 degree threads.

Basically at this point I know how to cut the threads. The things that I'm having trouble with still are simple and fixable.

My tool bit needs to be as sharp as possible. It looks very nice and I've gotten a lot of compliments on it. However, I annealed the tip at one point and even though I grinded it away, it's still affecting the bit. Also, it seems that every time I thread, I forget one little thing to do and the entire thing is ruined. Examples, the first time I threaded, I learned that taking off .007 with a thread file is easier than I thought. My second bar, I forgot to set the tool height, but fixed it , but didn't catch the thread in the right place. My third bar, I forgot to set the 29.5 degree angle, but everything else was perfect and my threads looked very nice. (i was quite upset). SO this time, I have a checklist printed out and I'm going to check everything before I start threading. Before I even start turning the steps and grooves, I'm going to set the compound rest to 29.5, just so I don't forget to do it when it's time to thread. SOund like a good plan?
 
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